<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        var a = 10;
        console.log('a=' + window.a); // a='10'
        delete window.a;
        console.log(window.a); // 10
        var obj = {
            name: 'wuchao',
            age: 26
        };
        console.log(obj.age); // 26
        delete obj.age;
        console.log(obj.age); //undefined
    </script>
</body>

</html>